It started small, just a handful of embers hiding in the hollow of a scribbly gum tree. Twelve metres high and perhaps 60 years old, the tree stood amid thick bush south of Lake Macquarie, on the NSW Central Coast, burled and knotty and gnawed by time. On September 30, 2013, it was set alight, along with the surrounding forest, during backburning, a defensive measure against a larger fire that had broken out earlier that day to the east.

In the following days, volunteers from the Rural Fire Service (RFS) moved through the backburned area, mopping up spot fires and flare-ups, their job complicated by the local geology, which is rich in coal and riddled, after 140 years of mining, with buried waste and disused collieries. The firefighters flooded the area with thousands of litres of water. But in this one scribbly gum, the water didn't get to where it should have. And so there remained a kernel of combustion, a dormant ball of ash which, encased in heartwood and starved of oxygen, gave off no smoke. As far as anyone could tell, the fire in the tree was out.

One week later, with the firefighters long gone, a branch from the tree fell off, loosing a shower of tiny embers, perhaps no bigger than a pin head. The embers wafted 18 metres before landing on an embankment of coal dust and leaf litter, causing it to smoulder steadily until, three days later, the embankment collapsed, setting alight the surrounding bush. It was October 17, two-and-a-half weeks after the back burning, and the real fire had begun.

Conditions that day were perfect for bushfires: 34 degrees, with wind gusts of up to 72km/h. Within minutes the fire had taken off, burning east towards the coast, torching a service station before moving into a state forest thick with gum trees. Surrounded at their base by confetti-like leaf litter, the gums went up in seconds, their bark peeling off in flaming streamers. Soon the fire was "crowning", bounding through the canopy at 100 metres a minute. Unable to stand within 40 metres without being burned, firefighters called in three waterbombing aircraft, to little avail.

Around mid-afternoon, the fire turned towards the township of Chain Valley Bay. "I got a call from a friend who was on his roof, and he could see it roaring toward us," says Lake Munmorah resident Marvin Campbell. Campbell and his 63-year-old neighbour, Walter Linder, began bucketing their homes. The smoke soon blocked out the sun. Campbell heard a series of loud booms – cans of paint and solvents in a nearby shed, exploding in the flames. At around 5pm, Campbell ran to check on Linder, who was lying on the ground, dead from a heart attack.

Wood burns at 240 degrees, but the fire was now 500 degrees, with flames 35 metres high. "At this point, all you can do is save yourself and protect property," says Rick Miller, an RFS fire investigator. Chief among that property was the heritage-listed village of Catherine Hill Bay, five kilometres to the north-east. "I was at my neighbour's, having a cup off tea," says resident Sue Whyte, "when I looked south and saw an enormous cloud of dense, angry-looking smoke." Within minutes police were banging on her door, telling her to grab her valuables and get out.

As flames approached the village, they tore through swathes of coastal heath, a low, hardy shrub that sent up colossal plumes of superfine ash, making the evening sky glow Armageddon orange. Embers showered the village, setting alight hundreds of tonnes of coal waste at the former Wallarah Colliery, and burning down the historic Jetty Master's Cottage. Next to go was Wallarah House, a $2 million homestead that had sat on a hilltop overlooking the village since 1889.

By midnight, after the loss of five properties, the fire was finally contained; it took another three days to extinguish. But Wallarah Colliery was another matter. It was burning five metres deep, too deep for water, which in any case might have flushed heavy metals and acids from the mine into nearby Lake Macquarie. And so, after three months, a long reach excavator was brought in to dig up the burning coal and spread it out to cool. Thus ended a fire that began as an ember, razed 2800 hectares of bushland, wiped out several homes and businesses, saw the death of Walter Linder, and caused the evacuation of an entire town.

Australia is among the most flammable countries in the world. According to NASA satellite data, there were an astonishing 4595 bushfires a week in Australia in 2013. The severity of such fires varies hugely, from tiny grassfires to catastrophic events like the 2009 Black Saturday bushfires that razed large parts of Victoria and caused the deaths of 173 people. It's for this reason that most districts in country Australia have their own RFS brigades made up of unpaid locals. NSW has more than 74,000 RFS members, making it the largest volunteer firefighting organisation in the world.

The Lake Macquarie region boasts 16 such brigades, including one at Wyee, a snoozy town on the southern shores of the lake. The brigade, which is based out of a battered green shed, has roughly 70 volunteers, one of whom was a local man named Alex Noble.

Noble joined the RFS in late 2011, when he was 18. Within no time he became one of the brigade's most dedicated members. Despite having a full-time job driving cranes, he was unstinting with his time, only too happy to perform any role, washing trucks, stowing hoses and sweeping out the shed.

In September 2013 he was roundly praised for single-handedly putting out a brush fire at the rear of his workplace, Eatons Building Materials, in Mannering Park on Wyee's semirural outskirts. That same month, he assisted Rick Miller with the investigation of a separate fire. "Alex was cooperative and appeared happy to help me," Miller says.

Noble has red, short-cropped hair and brown eyes. He is skinny: his work shorts and high-viz vest hung off him in folds. According to his grandfather, Paul Noble, Alex had few friends around town.

"He loved watching rugby league," says Paul, "so I encouraged him to join a local club, but he wasn't interested."

In the brigade, however, Alex was a star. He was invariably the first person to report to Wyee station after a fire was called in: once his RFS colleagues attended a bushfire only to find Noble already there, in his uniform. Fighting fires was his reason for being: he boasted about his training and experiences; his Facebook page featured a photo of himself set against a background of flaming treetops.

His Rural Fire Service work was voluntary, but he dreamed of one day becoming a paid firefighter with Fire and Rescue NSW. It didn't seem unreasonable. According to one observer, Noble was "the kind of kid who was really going places".

In late 2013, police noticed a significant increase in the number of bushfires in the Lake Macquarie area. More than 100 fires, most deemed suspicious or deliberate, had been reported between September 2012 and September 2013. The NSW Police Arson Unit subsequently established Strike Force Lorus,headed up by a thickset, 30-year-old detective named Chris Swadling.

The first thing Swadling did was plot the fires using the Arson Trends Analysis System. ATAS collates data provided by the RFS, Fire and Rescue NSW and police, and allows investigators to map when and where fires are occurring. "What we found was that most of the fires were clustered around Wyee," Swadling says. "Most were small roadside ignitions, which told us that it was probably someone who had a car. And most of them happened at night, which pretty much ruled out school kids." It was also unlikely to be farmers clearing scrub, Swadling says, since they get no benefit from roadside ignitions.

The fires mostly ranged in size from 10 square metres to 600 square metres; one was just two square metres. Swadling visited a number of the larger sites, together with Rick Miller, whose first job was to determine the fires' origins. Miller examined trees for scorch marks and rocks for soot stains. He also studied the grass. "As a general rule," he says, "the side of the tussock closest to the flames will burn hottest, and more of that will be gone than the other side, which will be higher and more intact. It's called the 'angle of char'."

Once you have the origin, you look for the cause. A big part of Miller's working life is spent on his hands and knees, fossicking through the dirt. "You're looking for any signs of cigarette butts, Jiffy lighters, accelerants. People also start fires with sparklers or mosquito coils, or with reactive chemicals. If you find a piece of exhaust carbon, then there's a chance there was some kind of mechanical cause."

Miller determined that most of the Wyee fires had been "hot sets", meaning they were started with an open flame, most likely from a cigarette lighter. ("Hardly anybody uses matches anymore.") Yet they found little in the way of evidence, which wasn't surprising. According to Detective Sergeant Hassan ElKhansa, a team leader in the Property Crime Squad's Arson Unit, the longer a fire burns, the more evidence it destroys. "This is the opposite to most other crimes, where the longer the offence goes on, the more evidence accumulates," he says. "It makes arson very difficult to investigate." (According to the NSW Bureau of Crime Statistics and Research, only 2.6 percent of arson cases result in legal action – among the lowest of all offences.)

Swadling had more luck when he looked at the phone data. When a member of the public reports a fire, they usually ring 000, in which case their number is automatically registered with Fire and Rescue NSW. (The call is also recorded.) Plenty of people had called 000 to report fires between September 2012 and September 2013, but one number kept popping up – 17 times, in fact. When Swadling traced the number, he found that it was subscribed to one Alex Gordon Noble.

Humans have for thousands of years been crucially dependent on fire. It enables us to cook and keep warm; it's a source of light, and has long been regarded by campers as a good substitute for television. In the case of arson, however, it can be a tool of unparalleled destruction. According to the Australian Institute of Criminology, bushfires injure more people in Australia than all other natural disasters combined. The insured losses from the 2009 Victorian fires alone exceeded $1 billion.

Arson is believed to be driven by four main factors: profit, revenge, mental illness and pyromania. "True pyromania is extremely rare," says professor James Ogloff, director of the Centre for Forensic Behavioural Science at Swinburne University in Melbourne. "I've seen hundreds of arsonists over my career, but only three or four pyromaniacs."

Pyromania was once thought to be a "moral illness" – an inability to distinguish right from wrong. Freud redefined it as a symptom of our desire to gain power over nature, adding that most pyromaniacs were males with a history of bed-wetting. Other possible causes were rejection and the wish for the return of an absent father. Nowadays pyromania is classified in the Diagnostic and Statistical Manual of Mental Disorders as an impulse-control disorder.

"For pyromaniacs, the fascination with fire is all-consuming," says Ogloff. "If they are not lighting fires, they are reading about fires or watching movies about fire – they love Backdraft. And once they start thinking about it, they have an uncontrollable need to light one. They then feel more relaxed, but, nine times out of 10, they also feel guilty."

Treatments for pyromania are largely ineffective, and usually come down to some form of cognitive behavioural therapy (replacing destructive thoughts with helpful ones). Locking people up doesn't seem to help, either. "Even in prison I've seen people who cannot stop lighting fires," says Ogloff. "In some low-security prisons you're allowed lighters, but in some prison smoking areas they have a hole in the wall where you light your cigarette. People sometimes put bits of paper in there, and light that. I've even seen people take a double-A battery and bread clips – the wire with plastic wrapped around it – and touch on both ends of the battery at the same time, and that gets hot enough to start a fire."

In the bushfire context, firefighters are in a catch-22 situation, Ogloff says. "They have to give fire warnings, but for people who are fascinated by fire, that's like a paedophile being near a kiddies' pool."

Detective Swadling now had a name, Alex Noble, and a phone number. From a senior RFS member who is permanently embedded with the arson unit, he'd also discovered that Noble was a Rural Fire Service member at Wyee. He then questioned everyone in the Wyee brigade, and listened back to Noble's 000 calls. "Not once did Alex identify himself to the 000 operator as an RFS member," Swadling says. "And not once did he tell his brigade mates that he was the one who had reported the fire."

Indeed, often Noble would light a fire, call 000 and wait for a notification on his RFS pager before racing to the station, where he would ask everyone where the fire was. On the afternoon of August 24, he did this on four separate occasions, lighting and then reporting fires at 2.20pm, 8.07pm, 9.49pm, and 11.54pm. When one of his fellow volunteers asked how he got to the station so quickly, Noble said he was living nearby, in Toepfers Road, Wyee. (In fact, he was living in Mannering Park, with his grandfather, 15 minutes drive south.)

"Alex was essentially leading a double life," Swadling says.

By early 2013, Noble was seeing a local woman named Sam. By September, with Sam heavily pregnant, the couple moved to a unit in Rutherford, a residential area an hour's drive north of Wyee, where Sam's family lived. On Monday, September 30, Noble resigned from his job, telling his workmates that he'd landed a full-time paid position with the Rutherford unit of Fire and Rescue NSW. (Actually, he'd got a job at a Rutherford building supplies company.)

Moving north meant Noble would no longer be attached to the Wyee brigade. (Rutherford doesn't have an RFS unit.) September 30, then, would be his last chance to light, and then fight, a bushfire. And so, during his lunch break, Noble walked to the rear of one of the company's sheds, where no one could see him. He crouched down in the dry grass, 30 centimetres inside the fence line, and lit a fire. He then walked back into the shed, and sat next to a fellow worker. Minutes later, he turned around and said: "Can you smell smoke?"

Swadling still didn't have enough to charge Noble and was planning to put him under surveillance. But the fire that day at Eatons forced his hand. Despite Noble's efforts with an extinguisher, the blaze got away. When crews from the RFS and Fire and Rescue NSW arrived, Noble joined in fighting the fire, before mysteriously disappearing at around 3pm. "He only wanted to light a small fire," says Rick Miller, "so when it got big he got upset."

Suspecting, correctly, that Noble had gone home, Swadling and another detective paid a visit to his Rutherford unit. "We asked Alex to come to the station and talk to us as a witness to the fire that day," Swadling says. "He was really excited at being able to assist."

Noble began the interview in high spirits, detailing what he'd seen that day, and his efforts to fight the fire. Swadling then asked Noble if he'd ever phoned 000 to report a fire. Yes, he said, once, about a year ago. Swadling then began playing the recordings of Noble's 17 calls to 000, the last of which was just four days before. Initially Noble said that he must have forgotten about the calls, but as the recordings went on, his face dropped. "He went from joking around with us to slumped over, head down, like his life's been ripped from him."

Noble left the station at about 10pm. Early the next morning, he phoned Swadling and said he wanted to talk. The two men met at Toronto Police Station, where they sat down in front of a printout of all the fires in the Wyee area. "Alex started freely admitting to all these fires," Swadling says. "He would've gone on but I made a mistake. I wish I didn't do it, but I said, 'You know, we're up to 10 fires now.' And then he stopped and said, 'That's all of them.' "

Alex Noble gave all sorts of reasons for lighting the fires. He lit them because he was bored. He lit them to gain experience as a firefighter. He lit them, almost as an afterthought, on his way home from dinner at the RSL; while driving back from a Westfield shopping centre; after dropping some DVDs at a mate's place; as he made his way home from a labouring job. Sometimes he lit his second, third or fourth fire for the day because the others he'd lit were "too small". He was fascinated by fire, his trial later heard: according to a psychiatrist's report, he was the rarest of arsonists: a true pyromaniac.

In October 2014, Noble was given two years' jail for deliberately lighting 15 fires in 2012 and 2013. In March this year, a court found that the fire he lit at Eatons on September 30, 2013 was the eventual cause of the October 17 blaze that led to the near annihilation of Catherine Hill Bay. He was subsequently sentenced to another eight years, and will be eligible for parole in October 2020.

Firefighters reserve particular contempt for arsonists within their ranks. RFS Commissioner Shane Fitzsimmons described Noble's conduct as "the ultimate betrayal". (None of Noble's brigade mates would talk for this story.) Wyee locals were similarly wounded: when news about Noble got out, his Facebook page received so much hate mail he had to shut it down.

Noble is currently in Cessnock jail; every two weeks his grandfather, Paul, visits him. "I still don't get it," Paul tells me. "Alex was never interested in fires as a kid." We are standing out the front of Paul's Mannering Park house, the small blue cottage he shared with his grandson. It starts to rain, so I say goodbye. Driving away, I pass the Country Women's Association hall; a caravan park. There are frangipani trees, and tall palms. On the edge of town, I spot a billboard by the roadside: "Bushfires," it reads. "Are you prepared?